1. Field of the Invention
The present invention relates to semiconductor devices and more particularly, to an improved high-k dielectric layer, a capacitor structure using the same, and an exemplary fabrication method thereof.
2. Description of the Prior Art
As known in the art, downscaling of the metal-insulator-metal capacitor for dynamic random access memory (DRAM) devices has required the introduction of high permittivity dielectrics, for example, titanium oxide (TiO2). It is well known that titanium oxide has multiple phases which have different dielectric constants. Two known phases of titanium oxide are anatase and rutile. It is often desirable to increase rutile TiO2 in the capacitor dielectric film because it has a much higher dielectric constant (k>90) than anatase TiO2.
Typically, TiO2 dielectric layer is deposited by using an atomic layer deposition (ALD) method. However, TiO2 is inherently formed in the anatase phase during the ALD process. To form a TiO2 dielectric layer with the rutile phase and low leakage as well, methods such as impurity doping, post annealing (600° C. or higher) and/or ozone-based ALD in combination with template layers are employed. However, the impurity doping method has problems such as high cost, low throughput and is hard to control its distribution. The drawback of the post annealing method is the additional thermal budget and mechanical stress, which may seriously degrade the MOS devices. The problems of the ozone-based ALD/template layer method include low deposition rate (˜0.4 Å per ALD cycle) and the risk of etching or oxidizing the underlying layer.
Water-based ALD method, which uses water vapor as oxidant in the ALD cycles, is also employed to deposit the TiO2 dielectric layer. The water-based ALD method has a much higher deposition rate than the ozone-based ALD method, meaning higher throughput. However, TiO2 deposited using the water-based ALD method is inherently in the anatase phase. To form rutile TiO2 in the water-based ALD process, a 10 nm thick TiO2 film or a relatively higher process temperature is typically required.
There is a need in this industry to provide an improved method for depositing a high-k dielectric material such as rutile TiO2 with a higher deposition/growth rate and a low leakage and without introducing the aforesaid prior art shortcomings.